Stall AOA not always lower for flaps down config
Stall occurs as a result of separation of the airflow over the upper surface of the wing. On most large commercial transport aircraft, extending of flaps involves not only lowering the wing's trailing edge, but also opening slots to allow airflow through the wing. This in combination with extended and/or gapped leading edges works to maintain attached airflow over the upper surface of the wing to a much higher AOA than with a clean wing configuration. A typical commercial transport wing may stall at less than 10 degrees AOA in the Flaps Up configuration while stall with Landing Flaps can be well beyond 20 degrees.